1. Field of the Invention
The present invention relates generally to relaying information in a communication system, and in particular to an apparatus and method for reconfiguring and broadcasting a neighbor Base Station (BS) advertisement message received from a serving BS by a relay station in a multi-hop relay Broadband Wireless Access (BWA) communication system.
2. Description of the Related Art
Currently, active research is being conducted to provide services with diverse Quality of Service (QoS) levels at about 100 Mbps to users in the 4th Generation (4G) communication system. Particularly, there is active research being conducted on providing high-speed service by ensuring mobility and QoS to a BWA communication system such as Wireless Local Area Network (WLAN) and Wireless Metropolitan Area Network (WMAN). Examples of such research are Institute of Electrical and Electronics Engineers (IEEE) 802.16d and IEEE 802.16e.
The IEEE 802.16d and IEEE 802.16e communication systems are implemented by applying Orthogonal Frequency Division Multiplexing (OFDM)/Orthogonal Frequency Division Multiple Access (OFDMA) to physical channels of the WMAN system. IEEE 802.16d considers only a single-cell structure with no regard to mobility of Subscriber Stations (SSs). In contrast, IEEE 802.16e supports the SS′ mobility to the IEEE 802.16d communication system. A mobile SS is called a Mobile Station (MS) or a Mobile Subscriber Station (MSS).
FIG. 1 illustrates the configuration of the conventional IEEE 802.16e communication system, configured in a multi-cell structure. Specifically, the system includes cells 100 and 150, base stations (BSs) 110 and 140 for managing the cells 100 and 150, respectively, and a plurality of MSs 111, 113, 130, 151 and 153. Signals are sent and received between the BSs 110 and 140 and the MSs 111, 113, 130, 151 and 153 in OFDM/OFDMA. The MS 130 exists in a cell boundary area between the cells 100 and 150, i.e. in a handover region. When the MS 130 moves to the cell 150 managed by the BS 140 during signal transmission/reception to/from the BS 110, the serving BS of the MS 130 changes from the BS 110 to the BS 140.
FIG. 2 illustrates an operation in a serving cell for broadcasting a Mobile_Neighbor-Advertisement (MOB_NBR-ADV) message in a cell in the conventional IEEE 802.16e communication system.
Referring to FIG. 2, a serving BS 210 collects information about its neighbor BSs 220 to 290 by communicating with them over a wired or wireless backbone network, and periodically broadcasts the neighbor BS information in a cell by a MOB_NBR-ADV message 214. Since the MOB_NBR-ADV message 214 is not intended for an MS at a particular location or in a particular direction within the cell, but is directed to all MSs within the cell, it delivers the neighbor BS information omni-directionally. An MS 212 recognizes the presence of the neighbor BSs 220 to 290 as well as the serving BS 210 by the MOB_NBR-ADV message 214. If the MS 212 is at a cell boundary between the serving BS 210 and the neighbor BS 230 as illustrated in FIG. 2, it does not need information about neighbor BSs in the opposite direction to the cell coverage, such as the neighbor BS 270. However, the serving BS 210 does not target the particular MS 212 in transmitting the neighbor BS information, and thus broadcasts the MOB_NBR-ADV message 214 across the cell. Although the MS 212 receives information about all of the neighbor BSs 220 to 290, it does not need information about the neighbor BSs 260 to 290 because they are not around the MS 212.
FIG. 3 illustrates a conventional multi-hop relay broadband wireless communication system. Referring to FIG. 3, an MS 309 is located at a cell boundary of a BS 301, though within the coverage area of the BS 301. Therefore, the MS 309 can receive a service from the serving BS 301 but with poor quality due to the distance constraint. Compared to an MS close to the serving BS 301, the MS 309 receives a service with a narrow bandwidth. Another MS 307 is outside the serving BS 301 and thus cannot communicate with the serving BS 301.
The application of a multi-hop relay scheme to both MSs 307 and 309 allows these MSs to receive a better-quality service in the manner of the MSs 311 and 313. As with the MS 309, the MS 311 is at the boundary of the service area of the BS 301. Yet, since a relay station (RS) 303 is located near the MS 311, the MS 311 can receive the service with higher quality than the MS 309 by communicating with the nearby RS 303 without the need for communication with the BS 301, though it is at the boundary of the service area of the BS 301. Like the MS 307, the MS 313 is outside the coverage of the BS 301, and cannot receive a signal or a service from the BS 301. Nonetheless, due to the existence of an RS 305 near the MS 313, the MS 313 can receive a service from the BS 301 via the RS 305.
In this manner, an MS which has difficulty in receiving a service or receives a poor quality service as illustrated in FIG. 2 can communicate with its serving BS outside the coverage area of the serving BS or receive a good-quality service from the serving BS through relaying of an RS as illustrated in FIG. 3.
Accordingly, there exists a need for reconfiguring the MOB_NBR-ADV message for effective communications among an MS, a BS and an RS in a multi-hop relay BWA communication system, when the pilot channel scanning procedure of FIG. 2 is adopted.